QUASI-BIENNIAL MODULATION OF THE SOUTHERN-HEMISPHERE STRATOSPHERIC POLAR VORTEX

Observations reveal that the wintertime southern hemisphere stratosphe ric polar vortex is modulated by the phase of the equatorial quasi-bie nnial oscillation (QBO). The high-latitude southern stratosphere is sh own to be slightly colder throughout the winter, and the final warming occurs later, when the QBO is in its west phase. During May-October, the modulation of winds by the QBO is confined to midlatitudes, at the edge of the polar vortex. The difference between west and east phase composites of zonal mean wind during November, at the time of the fina l warming in the southern hemisphere, exceeded 14 ms(-1). This differe nce is very similar to that in January in the northern hemisphere. Whi le northern hemisphere QBO effects are optimized using equatorial wind s near 40 hPa, southern hemisphere effects are best seen using similar to 25 hPa winds.